The present invention relates to imaging and, more particularly, to lenticular imaging systems. A particularly important aspect of the invention relates to optical reimaging of lenticular cards to produce real floating lenticular images without loss of desirable lenticular properties, such as the ability to produce the appearance of multi-frame action or three-dimensional images throughout complete image frames without multi-frame confusion.
Three-dimensional and/or floating image visual effects may be created by known holographic techniques, floating image projectors, handheld stereoscopic slide viewers, slide or movie projectors, and lenticular cards (transmissive or reflective types) for motion and/or three-dimensional (3D) simulation. Lenticular cards in the prior art are designed for unaided viewing and are typically located at arm""s length or beyond, at normal viewing distances from the eye. Such prior art lenticulars provide unsatisfactory images when they are projected or otherwise optically reimaged. In particular, ordinary lenticular objects reimaged by ordinary optical systems are severely limited in full-frame image capability, especially in the compact and optically powerful configuration necessary for hand-held floating image projectors.
A need exists for lenticular imaging systems and methods for producing lenticular cards and other products which provide improved images when optically reimaged.
Prior art lenticular cards and transparencies are designed for direct viewing. In the most common fabrication process, multiple image frames are selected and collated in the desired viewing order, then lines of data from each in turn are printed in successive strips oriented parallel to the lenticular cylindrical axis. Data strips from (for example) the bottom of each frame are printed behind the bottom cylindrical lenslet, or xe2x80x9clenticulexe2x80x9d, of the lenticular lens, and this process is iterated for all successive frame sections and lenticules until the appropriate data from all frame regions is printed behind the array of lenticules. This process is known as xe2x80x9cinterlacingxe2x80x9d. Each lenticule is associated with the same number of data strips as the number of frames, and each lenslet projects images of each of its associated strips at different angles, as shown in FIGS. 1-2. Equivalent direct imaging fabrication processes are also possible.
The picture elements or xe2x80x9cpixelsxe2x80x9d that make up each image frame consist of the variegated data (e.g., density, color, etc.) printed within each strip parallel to the lenticular cylindrical axis, combined with the independently variegated data printed perpendicular to that axis in the other corresponding strips associated with successive lenticules. With i data strips per lenticule corresponding to i image frames, and with y lenticules covering each data frame and x independent pixels in each data strip, the product xy represents the total number of pixels in each frame, and the product ixy is the total number of pixels printed in the entire ensemble of i frames.
Interlacing of the i data strips behind each lenticule follows essentially identical local mapping patterns throughout the lenticular. This results in iy image beams at i different angles for each orthogonal x-location. FIGS. 1 and 2 clarify this prior art.
Referring to the example of FIG. 1, the eye observes the top, center, and bottom of one section of an action-type lenticular in viewing a single frame, utilizing light that exits individual lenslets at different angles, depending on each pixel""s location within the frame. Such prior art lenticulars have their data strips interlaced such that an image beam from the strip corresponding to the top of the desired image frame is optically projected (typically but not necessarily at infinite conjugates) by the uppermost lenticule at an angle xcex1 to the optical axis (xcex1 in FIG. 1) that corresponds to the angle required for the observer""s eye to see the top of the desired frame. Similarly, data strips for the center, bottom, and all other regions of that frame are printed at the proper locations behind their associated lenticules such that their image beams are projected at the other angles appropriate for the observer""s eye to view those frame regions. As a result, all such image beams for a single frame are projected by the lenticular lens (the ensemble of all parallel lenticules) so that they intersect at the nominal eye location, as shown in FIG. 1. The observer therefore sees only the data from the data strips corresponding to the desired frame; the other data strip images are projected either above or below the eye in this example.
FIG. 2 illustrates a view of one individual lenslet, showing an example of how information corresponding to various frames is printed at each pixel location. Frame 1 data, for example, can be printed at a height h above the local lenticule axis, which relates to the focusing distance f (typically near or equal to the lenticule""s focal length), such that h=f tan xcex1. This example could therefore correspond to the topmost lenticule in FIG. 1, projecting the topmost frame data toward the observer at angle xcex1.
Moving the eye or moving/tilting the lenticular then allows successive frame data strip contributions from the various angles to be seen at each frame location. Thus, printing the appropriate multi-frame information within each pixel of the card or transparency produces the desired illusion (e.g., of motion, stereoscopic pairing, other action such as xe2x80x9cmorphingxe2x80x9d, or other desired effect) as the observer""s viewpoint changes. Note that while the examples of FIGS. 1 and 2 have been discussed in terms of xe2x80x9caction-typexe2x80x9d lenticulars with nominally horizontal lenticule axes, the principles are equally valid for xe2x80x9c3Dxe2x80x9d type lenticulars, in which the lenticule axes are nominally vertical, and in which selectively paired stereoscopic images are presented to the observer""s left and right eyes. (xe2x80x9cTop/bottomxe2x80x9d references would then be changed to xe2x80x9cleft/rightxe2x80x9d.)
Prior art lenticulars are optimized for unaided viewing. Thus, subsequent optical reimaging of such lenticulars necessarily alters the angular distribution of rays reaching the eye, with the effect of making truncated portions of several image frames visible simultaneously, thereby resulting in unintended confusion between frames. This typically truncates the effective angular size of a full frame as observed, since only part of each frame can be acceptably reimaged at any given combination of object orientation angle and eye position. Such alteration of angular distribution due to reimaging is qualitatively suggested in FIGS. 3-4, which use a simple lens to represent the possibly reflective and/or complex reimaging optics.
With no lens in FIG. 3, an eye at normal viewing distance from the lenticular object could directly view the top, center, and bottom of the frame in the manner of FIG. 1. (Without loss of generality, this eye location may conveniently be taken as that of the central lens in FIG. 3.) However, with the lens in place in FIG. 3, the eye must be located beyond the image (and also below the axis, as illustrated) in order to see the inverted end of the frame image. This is because reimaging by the lens causes the object beam, which is initially directed toward the optical axis, to be converted to the image beam, which is directed away from the axis. Note that the eye location shown is outside the viewing angle for rays from the opposite end of the frame, and that in fact, any eye location beyond the image necessarily precludes the observer from viewing the entire image simultaneously, because of similar viewing angle limitations. These are fundamental limitations on viewable frame size in directly viewed real images that can only be overcome when the lens is larger than the image, for example, as in FIG. 4.
As illustrated in FIG. 4, the eye can view the entire image from any of the eye locations shown (and from anywhere between them), because all rays between any eye location and any point on the image can be extended to intersect the optic, and can therefore be produced by the optic. Note that the perception of the same image point from different eye locations, as in location 1xe2x80x2, 2xe2x80x2, and 3xe2x80x2 on the right side of FIG. 4, utilizes different regions of the reimaging lens as well as significantly different emitting angles from the object. (For example, the angle between object ray 1 and the lens in FIGS. 4 is clearly much larger than that between the lens and corresponding image ray 1xe2x80x2.) It is clear from FIGS. 3 and 4 that prior-art lenticulars optimized for normal viewing distances cannot be properly reimaged by simple optical means (e.g., ordinary lenses, mirrors, etc.), because such reimaging introduces angular mapping changes that cause data from undesired frames to replace some of the desired data in the image. As a result, the observer is presented with multiple image frame bands that are each angularly truncated in the direction normal to the lenticular axis, resulting in multi-frame confusion.
Ordinary lenticular cards or transparencies are designed for images that are interlaced for normal viewing, with output beams projected at or near infinite conjugates. This is quite adequate for relatively long normal viewing distances beyond a foot or two because of the extremely short focal length of the lenticules (such as focal lengths typically well below 1 mm). However, inherent in the interlacing process, but never before recognized or exploited in the prior art, is the capability of drastically modifying the process to optimize the lenticular for optically-reimaged viewing.
Such modification is an object of the present invention. A need exists to optimize lenticulars for optical reimaging by modifying the interlacing process in a manner that preserves desired lenticular properties in the image. Another object of the invention is to incorporate desirable 3D or floating image properties, (e.g., similar to those provided by known volumetric display technology), in a hand-held or otherwise portable viewer. A further object is to incorporate real and virtual baffling techniques that are of particular value in optimizing image contrast in such viewers or in floating image projectors of any size. The preferred embodiments of the lenticular and the viewer incorporate these and other features, as the following description reveals.
A system and method are disclosed for generating lenticulars optimized for optical reimaging by compatible lenticular viewers or other optical instrumentation. The resulting images may then be reimaged without the truncation and multi-frame confusion inherent in the optical reimaging of prior-art lenticulars, thereby preserving desirable lenticular properties in the observed image. The lenticular viewer includes one or more optical elements positioned at predetermined optical distances from the specially-designed lenticular element, such that each one of the images from the lenticular element is reimaged in its intended full frame. In one embodiment, the lenticular viewer includes optics providing a viewing distance of less than about 18 inches from the lenticular element, which is particularly suitable for hand-held applications. The lenticular viewer may also be designed with the incorporation of a virtual baffling method which is also disclosed as part of this invention. This feature helps provide superior image contrast in many uncontrolled types of ambient illumination environments that might be encountered when using a hand-held viewer.
By modifying standard lenticular generation techniques known in the art, the disclosed system and method generate lenticular objects which are especially suitable for subsequent optical imaging, either as virtual images or as real screen-borne or directly viewed xe2x80x9cfloatingxe2x80x9d images. For such floating images, lenticulars may be used with known volumetric display technology to produce especially impressive real, floating, animated or autostereoscopic lenticular images.
The modified lenticulars may include minor focusing alterations to change their projected beam conjugates. However, it is of even greater (in fact, crucial) importance to significantly alter the mapping of the data strips, to match the lenticular-projected angles with the desired optical reimaging angles.
For example, in FIG. 4, the different object and image angles make it possible to print different temporal views at each point 1, 2, and 3 on the object, corresponding to the pixels intended to be reimaged at image angles and locations 1xe2x80x2, 2xe2x80x2, and 3xe2x80x2 respectively. The concept is the same as that illustrated by FIG. 2, but with the printed regions corresponding to the object angles for the reimaging of FIG. 4 rather than for the unaided viewing of FIG. 2.
These modifications to the lenticular design are more fully discussed in the detailed description of the preferred embodiment.
Note that by using commercially available components such as those specified in Table 1, a reasonable proof-of-principle design of specially-configured lenticulars and viewers implementing the lenticular-reimaging aspects of the disclosed system and method may be constructed.
Using, for example, the Rolyn 61.2825, a typical short projection of about 1.5 inches with a real-thickness beamsplitter is attained, providing an excellent vertical viewing angle of greater than about 48xc2x0 for small objects, with acceptable resolution. Of course, the preferred embodiment specified herein demonstrates the invention in a superior manner, with both a larger image and the incorporation of other disclosed viewer features such as the FIG. 10 off-axis background-suppression approach.